Cooling device, electronic apparatus, display unit, and method of producing cooling device

ABSTRACT

A cooling device includes a flow-path substrate, an intermediate substrate, and a lid-substrate each made of a polyimide resin, and a condenser substrate incorporated into holes of the intermediate substrate and an evaporator substrate which are made of a metal having a high thermal conductivity, whereby heat from a heat source can be enclosed into the evaporator substrate and the condenser substrate, so that the quantity of the latent heat can be substantially increased.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No.10/608,153, filed Jun. 30, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cooling device which is used toreduce the temperature caused by heat generated, e.g., from a driver ofa card type memory medium used in a personal computer, a digital camera,or the like, and to a method of producing the same. Moreover, thepresent invention relates to an electronic apparatus such as a personalcomputer, a digital camera, or the like, on which the cooling device ismounted.

2. Description of the Related Art

Storage media such as Memory Stick (registered trademark), Smart Media(registered trademark), Compact Flash (registered trademark), and soforth are small in size and thickness, and also the storage capacitiescan be considerably increased compared to conventional storage mediasuch as Floppy (registered trademark) disks or the like. Thus, they havebeen generally used in electronic apparatuses such as personalcomputers, digital cameras, and so forth. Regarding some of thesestorage media, flash memories integrated with drivers are used, ordrivers are mounted on the main parts of apparatuses, other cards, orthe like. For the storage media, recently, the capacities have beensignificantly increased. With increasing of the storage capacities ofthe storage media as described above, problems have arisen in that muchheat is generated to cause defects in operation.

Accordingly, it has been proposed that a cooling device is provided fora heat source in such an apparatus. For example, a cooling method usinga heat pipe has been proposed.

A heat pipe is a metallic pipe of which the inner wall has a capillarystructure, of which the inside is evacuated, and which tightly containsa small amount of water or a substitution Freon therein. When one end ofthe heat pipe is brought into contact with a heat source to be heated,the liquid contained therein is evaporated. Then, heat is taken into thegas as latent heat (evaporation heat). The heat is transferred to a lowtemperature region at a high speed (substantially equal to a soundvelocity). The gas is cooled to be returned to the liquid, and the heatis released (the heat is released due to the condensation latent heat).The liquid is passed through the capillary structure (or due to thegravity) to be returned to its original position. Thus, the heat can beefficiently transferred.

However, the related art heat pipe is tubular and voluminous.Accordingly, the heat pipe is unsuitable as a cooling device for use inelectronic apparatuses such as personal computers, digital cameras, andso forth for which reduction of the size and the thickness is required.

Accordingly, to reduce the size of the heat pipe, a cooling device hasbeen proposed in which grooves are formed on the surface of a siliconsubstrate and that of a glass substrate to be joined to each other, andthese substrates are joined to form the flow-path of a heat pipe betweenthe substrates. When the joining is carried out, a small amount of wateror a substitution Freon is introduced to be tightly kept. The phase ofthe water or Freon is changed in the heat pipe, so that the function ofthe heat pipe can be performed.

However, in the case in which the heat pipe is formed by use of asilicon substrate as described above, heat from an object to be cooledis diffused, since the thermal conductivity of the silicon itself ishigh. Thus, there are problems in that the evaporation of a liquid inthe heat pipe is insufficient, or the evaporation is not caused at all,so that the function of the heat pipe can not be carried out.

Moreover, electronic apparatuses having silicone substrates mountedthereon have problems in that they may be broken in event that theapparatuses drop.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide acooling device of which the cooling performance, the thermal stability,and strength are superior, an electronic apparatus and a display uniteach containing the cooling device, and a method of producing thecooling device.

According to a first aspect of the present invention, there is provideda cooling device which comprises a first substrate having groovesconstituting a heat pipe formed therein so as to be exposed to thesurface thereof, the grooves excluding at least the groove positioned incorrespondence to a wick, a second substrate made of a metal or amaterial having a thermal conductivity substantially equal to that of ametal, the second substrate having at least the groove for the wickformed at the surface thereof, said surface being joined to the firstsubstrate, and a third substrate into which the second substrate isincorporated so as to be exposed to the surface of the third substrate,said surface of the third substrate being joined to the first substrate,at least one of the first substrate and the third substrate being madeof a polyimide resin.

According to the present invention, the second substrate having a groovefor a wick formed on one side thereof is made of a material having athermal conductivity substantially equal to a metal. Thus, heat from aheat source can be efficiently transferred to the groove of the wick. Onthe other hand, the first substrate and so forth are made of a polyimideresin, so that the thermal conductivity is low. Thus, the heataccumulated in the wick is less diffused. Accordingly, the heat isenclosed in the wick, so that the quantity of the latent heat can besubstantially increased. Thus, the cooling performance of the heat pipecan be enhanced. In addition, the polyimide resin, which is thermallystable and flexible, is superior in strength. Thereby, the service lifeof the cooling device can be increased.

Preferably, the fourth substrate of the cooling device having at least agroove for a condenser formed on the surface thereof is made of a metalor a material having a thermal conductivity substantially equal to ametal. Thus, heat from a heat source can be efficiently transferred tothe groove of the condenser. On the other hand, the first substrate andso forth are made of a polyimide resin, so that the thermal conductivityis low. Thus, the heat accumulated in the wick is less diffused.Accordingly, the heat is enclosed in the condenser, so that the quantityof the latent heat can be substantially increased. Thus, the coolingperformance of the heat pipe can be enhanced.

Preferably, at least one of the second substrate and the fourthsubstrate is made of a metal containing copper or nickel. Therefore, theheat efficiency is enhanced.

Moreover, a thin film layer made of silicon or copper may be interposedbetween the one side of the first substrate and the one side of thethird substrate. Thereby, the first substrate and the third substrateeach made of a polyimide resin can be joined to each other via the thinfilms of silicon or copper or via an adhesive provided between the thinfilms. In this case, as the adhesive, a thermoplastic resin such as athermoplastic polyimide or the like is suitably used.

Preferably, the first substrate and the third substrate joined to eachother are physically separated from each other into a region containingthe second substrate and a region containing the condenser as acomponent of the heat pipe, and the cooling device further comprises aflexible substrate interposed between the separated regions and has aflow-path formed therein so as to connect the wick and the condenser toeach other. This enables the flow-path substrate for forming a heat pipeto have a flexible shape.

According to a second aspect of the present invention, there is provideda cooling device which comprises a first member having at least a wickas a component of a heat pipe, a second member physically separated fromthe first member and provided with a condenser as a component of theheat pipe, and a flexible substrate interposed between the first memberand the second member and having a flow-path for connecting the wick andthe condenser to each other formed therein, at least one of the firstmember and the second member being made of a polyimide resin. Thus, thewick member and the condenser member can be installed, even if they arenot arranged on a plane.

According to a third aspect of the present invention, there is provideda cooling device which comprises: a first substrate having open groovesconstituting a heat pipe formed therein, the open groove excluding atleast the open groove positioned in correspondence to a wick; a secondsubstrate made of a material having a thermal conductivity substantiallyequal to that of a metal, the second substrate having at least thegroove for the wick formed at the surface thereof, said surface beingjoined to the first substrate; a third substrate into which the secondsubstrate is incorporated so as to be exposed to the surface of thethird substrate, said surface of the third substrate being joined to thefirst substrate; and a lid-substrate joined to the surface of the firstsubstrate so as to cover said surface which is opposite to the side ofthe first substrate where the first substrate and the second substrateare joined to each other; at least one of the first substrate, the thirdsubstrate, and the lid-substrate being made of a polyimide resin.

Thus, the lid-substrate is brought in close contact with the opengrooves of the first substrate, so that the flow-path of a heat pipe canbe formed, and the thickness of the first substrate becomes that of theflow-path. Thus, the flow-path is substantially increased in size, sothat the performance of the heat pipe is increased.

Preferably, the flow-path for a working fluid, formed by joining of theopen grooves of the first substrate and the lid-substrate, has adiamond-like carbon film formed on the inner wall thereof.

In the cooling device of the present invention, at least one of thefirst substrate, the third substrate and the lid-substrate is made of apolyimide resin. The polyimide resin is water-absorptive to some degree.Accordingly, in the case in which the flow-path for a working fluid ismade of a polyimide resin, the durability can be increased by formationof such a diamond-like carbon film on the surface of the flow-path.

According to a fourth aspect of the present invention, there is providedan electronic apparatus which comprises: a slot to or from which a cardtype storage device containing a flash memory and a driver can beattached or detached; and a cooling device arranged adjacently to theslot, the cooling device comprising a first substrate having groovesconstituting a heat pipe formed therein so as to be exposed to thesurface thereof, the groove excluding at least the groove positioned incorrespondence to a wick, a second substrate made of a metal or amaterial having a thermal conductivity substantially equal to that of ametal, the second substrate having at least the groove for the wickformed at the surface thereof, said surface being joined to the firstsubstrate, and a third substrate into which the second substrate isincorporated so as to be exposed to the surface of the third substrate,said surface of the third substrate being joined to the first substrate,the first substrate and the third substrate being made of a polyimideresin.

The present invention may be applied as cooling devices for centralprocessing units of note-sizes personal computers, slots for attachmentof external storage units, and drivers for liquid crystal display unitsand so forth. Thereby, the cooling performance of these apparatuses canbe enhanced, and moreover, the apparatus can be given a high strength.

According to a fifth aspect of the present invention, there is provideda method of producing a cooling device which comprises the steps of amethod of processing a cooling device comprising the steps of forming afirst substrate made of a polyimide resin and having groovesconstituting a heat pipe formed therein so as to be exposed to thesurface thereof, the grooves excluding at least the groove positioned incorrespondence to a wick; forming a second substrate made of a metal ora material having a thermal conductivity substantially equal to that ofa metal, the second substrate having at least the groove for the wickformed on the surface thereof, incorporating the second substrate into athird substrate so as to be exposed to the surface of the thirdsubstrate, and joining the surface of the first substrate to the surfaceof the third substrate to each other. According to this invention, thecooling device having the above-described structure can be producedefficiently and securely.

Preferably, the method further comprises a step of incorporating thefourth substrate made of a metal or a material having a thermalconductivity substantially equal to that of a metal into the thirdsubstrate so as to be exposed to the surface of the third substrate.According to this structure, the condenser section is made of a materialhaving a high thermal conductivity, and thereby, heat can be effectivelytransferred.

The surface of the first substrate and that of the third substrate maybe melt-joined to each other by heating the first and second substrates.Accordingly, the joining can be securely carried out, and the costreduction becomes possible, due to the simple joining process.

Preferably, the method further comprises a step of forming adiamond-like carbon film in the grooves of first substrate. Thus, theservice life of the substrate made of a polyimide resin is enhanced. Thecooling performance is enhanced, due to the increased fluidity of theworking fluid.

According to a sixth aspect of the present invention, there is provideda method of producing a cooling device which comprises the steps offorming a first substrate having open grooves constituting a heat pipeformed therein, the open grooves excluding at least the open groovepositioned in correspondence to a wick, forming a second substrate madeof a metal or a material having a thermal conductivity substantiallyequal to that of a metal, the second substrate having at least thegroove for the wick formed on the surface thereof, joining a firstsurface of the first substrate to a lid-substrate to form a flow-pathfor a working liquid, incorporating the second substrate into a thirdsubstrate so as to be exposed to the surface of the third substrate, andjoining the surface of the third substrate to the second surface of thefirst substrate.

Thereby, the cooling device having the above-described structure can beproduced efficiently and securely.

Preferably, the method further comprises the steps of: forming a fourthsubstrate made of a metal or a material having a thermal conductivitysubstantially equal to that of a metal, the fourth substrate having atleast a groove for a condenser formed on the surface thereof, andincorporating the fourth substrate into the third substrate so as to beexposed to the surface of the third surface. Thereby, the heat-radiatingmeans (condenser) can be efficiently incorporated in the device.

Preferably, the step of forming the flow-path for a working fluidincludes a step of forming a diamond-like film on the surface of theflow-path. Thereby, the cooling device of which the substrates haveenhanced durability and cooling performance is produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing the structure of acooling device according to the present invention;

FIG. 2 is a cross-sectional view of the assembled cooling deviceaccording to the embodiment of the present invention;

FIG. 3 consists of plan views of the respective substrates of thecooling device according to the embodiment of the present invention;

FIG. 4 is a plan view of the cooling device according to the embodimentof the present invention which is assembled by the flow-path substrate,the intermediate substrate, the condenser substrate, and the evaporatorsubstrate;

FIG. 5A is a perspective view of a silicon substrate;

FIG. 5B is a perspective view of a resin substrate;

FIG. 5C is a perspective view of a polyimide resin—metal compositesubstrate according to the present invention which is compared to thesilicon substrate of FIG. 5A and the polyimide resin substrate of FIG.5B from the standpoint of the thermal diffusion properties;

FIG. 6 illustrates a process of producing the cooling device of thepresent invention;

FIGS. 7A, 7B, 7C, 7D, and 7E schematically show a process of forming aflow-path substrate for use in the cooling device of the presentinvention;

FIGS. 8A, 8B, 8C, and 8D schematically show a process of forming acondenser substrate and an evaporator substrate for use in the coolingdevice of the present invention;

FIG. 9 schematically shows a process of joining the flow-path substrateand a lid-substrate to each other which are used in the cooling deviceof the present invention;

FIG. 10 schematically shows a process of incorporating the condensersubstrate and the evaporator substrate into an intermediate substratefor use in the cooling device of the present invention;

FIG. 11 schematically shows a process of joining the flow-path substrateand the intermediate substrate to each other, the flow-path substratehaving the lid-substrate joined thereto, the intermediate substratehaving the condenser substrate and the evaporator substrate joinedthereto;

FIG. 12 schematically shows a cooling device according to anotherembodiment of the present invention;

FIG. 13 is a schematic perspective view of a personal computer on whichthe cooling device of the present invention is mounted; and

FIG. 14 is a schematic perspective view of a liquid crystal display uniton which the cooling device of the present invention is mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

(Cooling Device)

FIG. 1 is a perspective view of a cooling device according to thepresent invention which is in the dissembled state. FIG. 2 is across-sectional view of the cooling device which is in the assembledstate.

As shown in FIGS. 1 and 2, a cooling device 1 comprises five substrates10, 20, 30, 40, and 50. The flow-path substrate 10, the intermediatesubstrate 30, and the lid-substrate 50 are rectangular and are made of apolyimide resin which is not thermoplastic. The condenser substrate 20and the evaporator substrate 40 are rectangular substrates, e.g., madeof a metal with a high thermal conductivity such as copper or the like.The condenser substrate 20 and the evaporator substrate 40 areincorporated into holes 31 and 32 of the intermediate substrate 30,respectively. Regarding these five substrates 10, 20, 30, 40, and 50,the joining surfaces thereof are covered with a copper thin film (notshown in the drawings), respectively. These substrates are secured toeach other by hot-press joining via an adhesive layer 60 of athermoplastic polyimide resin (e.g., Upilex VT, manufactured by UbeIndustries Ltd., etc.). Grooves 21 are formed on the surface 20 a of thecondenser substrate 20, and grooves 41 are formed on the surface 40 a ofthe evaporator substrate 40. An open groove 11 is formed in theflow-path substrate 10. Moreover, holes 31 and 32 are formed in theintermediate substrate 30. The grooves 21 and 41, the open groove 11,and the holes 31 and 32 are formed by bonding so as to function as aloop-shaped heat pipe.

Hereinafter, the constitution of the grooves 21 formed in the condensersubstrate 20, the grooves 41 formed in the evaporator substrate 40, theopen groove 11 in the flow-path substrate 10, and the holes 31 and 32 inthe intermediate substrate 30, and the lid-substrate 50 will bedescribed with reference to FIG. 3.

As shown in FIG. 3, a copper thin-film (not shown) is formed on thesurface of the lid substrate 50 which is to be bonded to the flow-pathsubstrate 10.

The open grooves 11 are formed in the flow-path substrate 10 so as topass through the flow-path substrate 10, respectively. The open grooves11, when they are bonded to the lid-substrate 50 via the adhesion layer60, form a liquid phase path 12 through which the liquid flows as aworking fluid, a gas phase path 15 through which the gas flows as theworking fluid, and a reservoir 13 in which the liquid is stored andsupplied. Thin-films (not shown) of diamond-like carbon (hereinafter,referred to as DLC) may be formed in the liquid phase path 12, the gasphase path 15, and the groove of the reservoir 13, which are formed byusing the lid-substrate 50 and the flow-path substrate 10. The polyimideresin, which is a material for the lid-substrate 50 and the flow-pathsubstrate 10, is water-absorptive to some degree. Thus, problematically,the substrate 50 and 10 may be distorted. The thin-film layers made ofDLC function as protecting films, and thereby, the cooling device 1 hasa superior durability.

The holes 31 and 32 are formed in the intermediate substrate 30 so as topass through the intermediate substrate 30.

The grooves 21 are formed on the surface 20 a of the condenser substrate20. The grooves 21 function as a condenser which condenses the gasintroduced therein through the gas phase path 15 into the liquid, andcirculates the produced liquid to a low temperature portion 16.

The grooves 41 are formed on the surface 40 a of the evaporatorsubstrate 40. The grooves 41 function as a cooling portion. The grooves41 function so that the liquid introduced through the liquid phase path12 or the reservoir 13 into the groves 41 is evaporated, and theproduced gas is flown into an evaporation portion 14.

FIG. 4 shows the substrates 10, 20, 30, 40, and 50 which are joined toeach other.

A liquid is placed and kept tightly inside of the heat pipe which isformed by joining the substrate 10, 20, 30, 40, and 50. The liquidtightly enclosed in the heat pipe is circulated while it is changed fromits gas phase to its liquid phase, and vice versa in the heat pipe,whereby heat transfer is carried out. Thus, the cooling device 1functions.

Hereinafter, the circulation of the liquid and the gas is described, inwhich the circulation starts at the liquid phase path 12 forconvenience' sake.

First, the liquid is flown into the evaporation portion 14 through theliquid phase path 12. In this case, if the quantity of the liquid flowninto the evaporation portion 14 is smaller than a predetermined amount,a liquid in such an amount as compensates for the deficiency is suppliedfrom the reservoir 13 so that the drying out is prevented.

The liquid flown into the evaporation portion 14 is heated to boil. Thegas, which is produced by the boiling, is flown into the low temperatureportion 16 via the gas phase path 15, and is condensed into the liquid.The liquid, produced by the condensation, is flown from the lowtemperature portion 16 into the liquid phase path 12 to be circulated.

According to this embodiment, the condenser substrate 20 and theevaporator substrate 40 are made of copper. However, as the materialsfor the substrates 20 and 40, silicon, nickel, or the like may be used.

FIGS. 5A, 5B, and 5C schematically show the areas where heat is diffusedon substrates in a predetermined time, respectively. FIG. 5A shows thediffusion of heat on a silicon substrate. FIG. 5B shows that on apolyimide resin substrate. FIG. 5C shows that on a composite substratecomprising a polyimide resin and a metal, such as copper incorporatedinto a polyimide resin substrate.

As shown in FIG. 5A, heat from a heat source A-1 for the siliconsubstrate is diffused in a wide area as shown by arrows (A-2) in FIG.5A. On the other hand, as shown in FIG. 5B, heat from a heat source B-1for the polyimide substrate is not widely diffused in a wide area asshown by the arrows in FIG. 5B (the heat is diffused in a region B-2).

A predetermined quantity or more of heat is required to be concentratedto the evaporator so that the heat pipe can function. In the case inwhich the substrate is made of a silicon material as shown in FIG. 5A,the function of the heat pipe can not be sufficiently carried out, sinceheat is excessively diffused.

Furthermore, the evaporator is required to have a thermal conductivityof a predetermined value or higher, so that the heat pipe can function.As shown in FIG. 5B, the thermal conductivity of the substrate made of apolyimide resin only is substantially zero, the function of the heatpipe can not be sufficiently carried out.

On the other hand, according to the present invention, as shown in FIG.5C, heat from the heat source C-1 in the polyimide resin—metal compositesubstrate is highly diffused in the metal portion, and is hardlydiffused in the polyimide resin region in the periphery of the metalportion (C-2). Thus, the heat is sufficiently transferred in theevaporator, while the heat is difficult to be diffused in thesurrounding polyimide resin portion. Therefore, the heat is concentratedto the evaporator. Thus, the function of the heat pipe can besatisfactorily carried out.

The cooling device 1 of the present invention comprises the flow-pathsubstrate 10, the intermediate substrate 30, and the lid-substrate 50which are made of a polyimide resin, respectively, and the condensersubstrate 20 and the evaporator substrate 40 which are made of a metalhaving a high thermal conductivity, and are incorporated into the holes31 and 32 of the intermediate substrate 30, respectively.

According to the above-described constitution, the evaporator substrate40 having the grooves of the wick is made of a metal or a materialhaving such a high thermal conductivity as that of the metal, so thatheat from a heat source can be transferred to the grooves of the wick athigh efficiency. On the other hand, the flow-path substrate 10, theintermediate substrate 30, the lid-substrate 59, and so forth, made of apolyimide resin, have a low thermal conductivity. Thus, the heat storedin the wick is less diff-used, i.e., the heat is enclosed. Thus, thequantity of the latent heat can be substantially increased, so that thecooling performance of the heat pipe can be enhanced. Moreover, thepolyimide resin is thermally stable and also is flexible. Thus, theresin is superior in strength, so that the service life of the coolingdevice 1 can be increased.

(Method of Producing Cooling Device)

FIG. 6 illustrates processes of producing the cooling device.

First, the open grooves 11 are formed in the flow-path substrate 10, andthe holes are formed in the intermediate substrate 30. The grooves andthe holes function as a heat pipe (step 601). The open groove 11 isformed at the surface 10 a of the flow-path substrate 10 made of apolyimide resin. The open groove 11 functions as the liquid phase path12, the gas phase path 15, the reservoir 13, the evaporation portion 14,and the low temperature portion 16. The holes 31 and 32 are formed inthe intermediate substrate 30, which is made of a polyimide resin, so asto pass through the intermediate substrate 30.

FIGS. 7A to 7E show a process of forming the flow-path substrate 10 asan example of the step 601.

FIG. 7A shows the flow-path substrate 10 before the processing, having athickness of about 25 to 1000 μm.

Then, as shown in FIG. 7B, copper thin films 70 are formed on both ofthe sides of the flow-path substrate 10 which are to be bonded to theintermediate substrate 30 and the lid-substrate 50, respectively.Regarding a method of forming the copper thin-films 70, both of thesides of the flow-path substrate 10 are processed with oxygen-plasma forsurface-modification of the substrate. Then, the copper thin films 70are formed thereon by vapor-deposition using sputtering so as to have athickness of about 50 nm to 1 μm.

Next, the formed flow-path substrate 10 having the copper thin-film 70as shown in FIG. 7C is placed into a vacuum hot press machine, and heatat a temperature of 150° C. to 350° C. is applied to the substrate undera reduced pressure of about 10⁻⁴ Torr to 10 Torr. An adhesion layer 60is fixed to the bonding surface of the lid-substrate 50 at a pressure of2 to 60 kg/cm² by hot-press bonding.

Next, as shown in FIG. 7D, the flow-path substrate 10 is set in a lasermachine, and the third harmonic by YAG laser is irradiated thereto fromone side of the flow-path substrate 10 to work the substrate 10. In thiscase, it is necessary to input a desired pattern for the flow-pathsubstrate 10 into the laser machine in advance.

Then, as shown in FIG. 7E, the open groove 11 is formed in the flow-pathsubstrate 10 so as to be passed trough the substrate 10 in the desiredpattern by means of the third harmonic by the laser.

The method of forming the open groove 11 in the flow-path substrate 10is described above. Regarding the intermediate substrate 30, the copperthin-film and the adhesion layer 60 are formed in the same manner asdescribed above, and then, holes are formed by laser-machining in thesame manner as described above. Moreover, regarding the lid-substrate50, the copper thin-film 70 is formed on the bonding surface thereof forthe flow-path substrate 10. For the lid-substrate 50, it is not requiredto form holes. Thus, laser machining is not carried out.

Next, grooves are formed on the condenser substrate 20 and theevaporator substrate 40 so that the function of the heat pipe can berealized (step 602).

First, as shown in FIG. 8A, a resist layer 81, e.g., made of SU 8, whichis an organic material, is formed on a plate 82. A resist layer 83 isformed thereon in a pattern. The plate 82 and the layers 81 and 83constitute a pattern substrate 80.

Thereafter, as shown in FIG. 8B, UV rays are irradiated from the upperside of the pattern layer 80 so that the resist layer 81 is etched.

Next, as shown in FIG. 8C, the resist layer 83 is peeled off from thepattern substrate 80. A copper layer 84 is formed on the formed surfaceby electro-forming of copper.

Then, the copper layer 84 is peeled off from the pattern substrate 80 asshown in FIG. 8D. The formed copper layer 84 constitutes each of thecondenser substrate 20 and the evaporator substrate 40 each havinggrooves.

In the next process of the production of the cooling device, theflow-path substrate 10 and the lid-substrate 50 are joined to each otherby hot press joining (step 603).

As described above, the flow-path substrate 10 and the lid-substrate 50are joined to each other via the copper thin-films and the adhesionlayer 60, which are formed on the bonding surfaces thereof, by applyinga pressure of 2 to 60 kg/cm² under a reduced pressure of 10⁻⁴ Torr to 10Torr, at a temperature of 150 to 350° C., and for 5 to 15 minutes.

After the flow-path substrate 10 and the lid-substrate 50 are joined toeach other, a thin film of DLC (not shown) is formed on the surface ofthe produced flow-path for a working fluid (step 604).

In particular, first, a copper thin film is embedded into the surface ofthe groove as the working fluid flow-path, which is formed in the step603, and is introduced into a PBII apparatus. Oxygen ions are implantedinto the surface of the groove to modify the copper surface. The portionnot to be processed of the working fluid flow-path, i.e., the portionexcluding the groove, is protected by a metal mask or a resist mask as aprotecting film. The flow-path substrate 10 and the lid-substrate 50 areplaced in the center of the vacuum apparatus and are connected to apulse electric source via an insulator. The vacuum apparatus isevacuated by means of a vacuuming pump. Moreover, oxygen, methane,nitrogen, titanium, or the like is converted to the pulse plasma at anion source to be supplied synchronously with the pulse. As describedabove, the portion not to be processed is protected by the protectingfilm. Accordingly, the DLC thin film can be formed in the region to beselectively processed, i.e., the groove of the working fluid flow-pathonly. Methane gas supplied from the ion source is converted to itspulse-plasma. Thus, the DLC thin film with a thickness of 3 μm is formedon the modified surface of the groove of the working fluid flow-path.The contact angle of water to the surface is 70 degrees. Moreover, CF₄gas supplied from the ion source is converted to its pulse-plasma, andis ion-implanted for about 3 minutes, so that fluorine is substitutedfor the hydrogen at the surface. In this case, the contact angle ofwater to the surface becomes 110 degrees. Thus, the DLC thin film isformed on the groove for the working fluid flow-path. The oxidation ofthe copper is described above. In the case in which titanium is usedinstead of copper and is implanted, similar results are also obtained.

As shown in FIG. 10, the condenser substrate 20 and the evaporatorsubstrate 40 are joined to the holes 31 and 32 of the intermediatesubstrate 30, respectively (step 605).

In particular, the condenser substrate 20 and the evaporator substrate40 are incorporated into the intermediate substrate 30 having theadhesion layer 60 made of a thermoplastic polyimide resin formed on thebonding surface, from the bonding surface side of the substrate 30, andare joined thereto by application of a pressure of 2 to 60 kg/cm² at apredetermined temperature of 150 to 350° C. for 5 to 150 minutes underthe reduced pressure condition of 10⁻⁴ to 10 Torr.

Finally, as shown in FIG. 11, the flow-path substrate 10 to which thelid-substrate 50 is joined is joined to the intermediate substrate 30 towhich the condenser substrate 20 and the evaporator substrate 40 arejoined as described above (step 606).

In particular, the intermediate substrate 30 having the copper thin filmand the adhesion layer 60 made of a thermoplastic polyimide resin formedon the bonding surface thereof is joined to the flow-path substrate 10by pressing at a pressure of 2 to 60 kg/cm² at a temperature of 150 to350° C. for 5 to 15 minutes under the reduced pressure of 10⁻⁴ to 10Torr.

In this embodiment, as the material for the condenser substrate 20 andthe evaporator substrate 40, copper is used. Other materials such assilicon, nickel, or the like may be used.

In this embodiment, for the adhesion layer 60, a thermoplastic polyimideresin is used. A thermosetting polyimide resin may be used. In the case,the thermosetting polyimide resin is cured by heating. Thus, suitably,the adhesion layer 60 is heated in the final stage of the joining.

Moreover, according to this embodiment, laser processing is employed forforming of the open groove 11 in the flow-path substrate 10 and theholes 31 and 32 in the intermediate substrate 30. These groove and holesmay be formed by forming using a mold, i.e., by hot embossing or thelike. In this case, the open groove 11, which is formed in the flow-pathsubstrate 10 so as to be passed through the substrate 10 as describedabove, are not limited to the open groove, and may be formed as anordinary groove. In the case in which the groove 11 is formed as anordinary groove, the lid-substrate 50 and the adhesion layer 60 becomeunnecessary. Thus, the device can be reduced in thickness. Also,preferably, the DLC thin film is formed on the groove which constitutesthe flow-path of the heat pipe.

Referring to the processing of the open groove 11 of the flow-pathsubstrate 10 and the holes 31 and 32 of the intermediate substrate 30,etching (chemical etching using an alkali solution of hydrazine, KOH, orthe like, or plasma-etching using oxygen plasma), sand-blasting, and soforth may be employed.

According to this embodiment, for formation of the condenser substrate20 and the evaporator substrate 40, a UV-LIGA method is used. Theformation may be carried out by photo-etching, machining, reactive ionetching (RIE) or the like.

The heat pipe can be efficiently produced according to theabove-described production methods.

(Other Example of Cooling Device)

FIG. 12 shows a flexible cooling device 120 in which a condenser member122 and an evaporator member 124 are connected to each other via aflexible substrate 121.

The condenser member 122 and the evaporator member 124 are made of apolyimide resin, respectively. The condenser substrate 20 and theevaporator substrate 40 are incorporated therein by the above-describedmethod.

The flexible substrate 121 is made of a plastic, and contains theflow-path 123 of a heat pipe. These members and the substrates areintegrated to form the heat pipe.

The flexible substrate 121 can be desirably deformed. For example, theevaporator member 124 fixed, e.g., to a heating unit of an electronicapparatus, and the flexible substrate can be disposed so as to beextended in close contact with the surface features of the electronicapparatus.

According to the above-described structure of the cooling device, theheat pipe can be efficiently installed even in a narrow space. Thus, thesize or thickness of the electronic apparatus or the like can bereduced.

(Electronic Apparatus)

FIG. 13 is a schematic perspective view of a personal computer in whichthe cooling device of the present invention is mounted.

A personal computer 130 contains a slot 131 to or from which a storagemedium 134 having a flash memory 133 and a driver 132 is attached ordetached, and a central processing unit (CPU) 135. The cooling device 1of the present invention is arranged in the personal computer 130 sothat the wick is positioned, e.g., under the driver 132 of the storagemedium 134 which is disposed in the slot 131.

Also, the cooling device 1 of the present invention may be arranged sothat the evaporator is positioned adjacently to the central processingunit 135. In this case, the condenser is suitably positioned adjacentlyto a cooling fan or the like (not shown). Thereby, heat generated fromthe central processing unit 135 is absorbed by the evaporator. The heatis released from the condenser due to the action of the cooling fan.Thus, the central processing unit 135 can be cooled.

In the above-description, the personal computer is referred to as anexample of the electronic apparatus. The cooling device of the presentinvention may be mounted onto other electronic apparatus such as adigital camera, a video camera, or the like.

(Display Unit)

FIG. 14 is a schematic perspective view of a liquid crystal display unitonto which the cooling device of the present invention is mounted.

A liquid crystal display unit 140 contains a driver 141, a displaysection 142, and a cooling fan 143. The cooling device 1 of the presentinvention is arranged in the liquid crystal display unit so that theevaporator is positioned adjacently to the driver 141, and the condenseris positioned adjacently to the cooling fan 143. The heat generated fromthe driver 142, caused by the operation of the liquid crystal displayunit 140, is absorbed by the evaporator. The absorption heat causes theliquid in the cooling device 1 to be evaporated and flows into thecondenser via the flow-path. The cooling fan 143 cools the condenser sothat the heat of the gas flown into the condenser is released, and thegas is liquefied again. The liquid, produced in the condenser, is flowninto the evaporator via the flow-path, and absorbs the heat generatedfrom the driver 141 to be evaporated again. The driver 141 can be cooledby the above-described circulation of the liquid in the cooling device1. Similarly, the display section 142 can be cooled by disposing theevaporator adjacently to the display section 142.

1. A cooling device comprising: a first member having at least a wick asa component of a heat pipe; a second member physically separated fromthe first member and provided with a condenser as a component of theheat pipe, the first member and the second member having channels madeof at least one of a metal and a material having a thermal conductivitysubstantially equal to that of a metal; and a flexible substrateinterposed between the first member and the second member and having aflow-path formed therein so as to connect the wick and the condenser toeach other, the flow-path formed in the flexible substrate has adiamond-like carbon film formed therein, wherein at least one of thefirst member and the second member being made of a polyimide resin. 2-3.(canceled)